The nature of switch cost: task set configuration or carry-over effect?

Switching between simple response-sets: inferences from the lateralized readiness potential

When the lateralized readiness potential (LRP) is recorded in stimulus-response compatibility (SRC) tasks, two processes may overlap in the LRP, stimulus-driven response priming and activation based on response selection rules. These overlapping processes are hard to disentangle with standard analytical tools. Here, we show that Residue Iteration Decomposition (RIDE), based on latency variability, separates the overlapping LRP components from a Simon task into stimulus-driven and response-related components. SRC affected LRP amplitudes only in the stimulus-driven component, whereas LRP onsets were affected only in the response-locked component. Importantly, the compatibility effect in reaction times was more similar to the effect in the onsets of the RIDE-derived response-locked LRP component than in the unseparated LRP. Thus, RIDE-separated LRP components are devoid of distortions inherent to standard LRPs.

Long reaction times (RT) paradoxically occur with extremely loud auditory stimuli ( Van der Molen & Keuss, 1979 , 1981 ) or with ultrabright and large visual stimuli ( Jaśkowski & Włodarczyk, 2006 ) when the task requires a response choice. Van der Molen and Keuss (1981 ) hypothesized that this effect results from an arousal-driven elongation of response-selection processes. We tested this hypothesis using visual stimuli and chronopsychophysiological markers. The results showed that the latency of both early (P1 recorded at Oz) and late (P300) evoked potentials decreased monotonically with intensity. In contrast, the latency of stimulus-locked lateralized readiness potentials (LRP) abruptly increased for the most intense stimuli, thus mirroring the reaction time–intensity relationship. Response-locked LRPs revealed no dependency on intensity. These findings suggest that the processes responsible for the van der Molen-Keuss effect influence processing stages that are completed before the onset of LRP. The van der Molen-Keuss effect likely occurs later than those represented by early sensory potentials. This is in keeping with the hypothesis of van der Molen-Keuss.

Pre-stimulus EEG effects related to response speed, task switching and upcoming response hand

Motor-response generation as a source of aging-related behavioural slowing in choice-reaction tasks

Abnormalities in motor skills have been regarded as part of the symptomatology characterizing autism spectrum disorder (ASD). It has been estimated that 80 % of subjects with autism display "motor dyspraxia" or clumsiness that are not readily identified in a routine neurological examination. In this study we used behavioral measures, event-related potentials (ERP), and lateralized readiness potential (LRP) to study cognitive and motor preparation deficits contributing to the dyspraxia of autism. A modified Posner cueing task was used to analyze motor preparation abnormalities in children with autism and in typically developing children (N = 30/per group). In this task, subjects engage in preparing motor response based on a visual cue, and then execute a motor movement based on the subsequent imperative stimulus. The experimental conditions, such as the validity of the cue and the spatial location of the target stimuli were manipulated to influence motor response selection, preparation, and execution. Reaction time and accuracy benefited from validly cued targets in both groups, while main effects of target spatial position were more obvious in the autism group. The main ERP findings were prolonged and more negative early frontal potentials in the ASD in incongruent trials in both types of spatial location. The LRP amplitude was larger in incongruent trials and had stronger effect in the children with ASD. These effects were better expressed at the earlier stages of LRP, specifically those related to response selection, and showed difficulties at the cognitive phase of stimulus processing rather that at the motor execution stage. The LRP measures at different stages reflect the chronology of cognitive aspects of movement preparation and are sensitive to manipulations of cue correctness, thus representing very useful biomarker in autism dyspraxia research. Future studies may use more advance and diverse manipulations of movement preparation demands in testing more refined specifics of dyspraxia symptoms to investigate functional connectivity abnormalities underlying motor skills deficits in autism.

SummaryThe neural responses that distinguish novel from familiar items in recognition memory tasks are remarkably fast in both humans and nonhuman primates. In humans, the earliest onsets of neural novelty effects emerge at about ∼150–200 ms after stimulus onset [1–5]. However, in recognition memory studies with nonhuman primates, novelty effects can arise at as early as 70–80 ms [6, 7]. Here, we address the possibility that this large species difference in onset latencies is caused experimentally by the necessity of using reward reinforcement to motivate the detection of novel or familiar items in nonhuman primates but not in humans. Via magnetoencephalography in humans, we show in two experiments that the onset of neural novelty signals is accelerated from ∼200 ms to ∼85 ms if correct recognition memory for either novel or familiar items is rewarded. Importantly, this acceleration is independent of whether the detection of the novel or the familiar scenes is rewarded. Furthermore, this early novelty effect contributed to memory retrieval because neural reward responses, which were contingent upon novelty detection, followed ∼100 ms later. Thus, under the contextual influence of reward motivation, behaviorally relevant novelty signals emerge much faster than previously held possible in humans.

Cognitive control processes, such as updating task-relevant information while switching between multiple tasks, are substantially impaired in older adults. However, it has also been shown that these cognitive control processes can be improved by training interventions, e.g., by training in task switching. Here, we applied an event-related potential (ERP) approach to identify whether a cognitive training improves task-preparatory processes such as updating of relevant task goals. To do so, we applied a pretest-training-posttest design with eight training sessions. Two groups of older adults were either trained in task switching (treatment group) or in performing single tasks (control group) and we compared their performance to a group of untrained younger adults. To foster cue updating in the treatment group, we applied a cue-based switching task in which the two task cues were randomly selected prior to target presentation so that participants had time to prepare for the upcoming task. In contrast, the control group also received task cues but those were redundant as only one task had to be performed. We also examined whether training in cue updating during task switching can be transferred to a similar cognitive control task measuring updating of context information, namely a modified version of the AX-Continuous Performance Task (AX-CPT). The results revealed training-specific improvements in task switching, that is, a larger improvement in blocks requiring switching in comparison to single tasks at the behavioral level. In addition, training specific-effects were also found at the neuronal level. Older adults trained in cue updating while switching showed a reduction in mixing costs in the cue-related P3, indicating an improvement in preparatory updating processes. Additionally, P3 topography changed with training from a very broad to a parietally focused scalp distribution similar to the one found in younger adults. However, we did not obtain training-specific improvements in context updating in the AX-CPT neither at the behavioral level nor at the neuronal level. Results are discussed in the context of the ongoing debate on whether transfer of cognitive training improvements is possible.

The present study explored the impact of the stimulus presentation rate on sequential effects in event-related potentials (ERPs) and reaction times (RTs). Random series of equiprobable tones were presented at interstimulus intervals (ISIs) of 1.3, 2.1, and 2.9 s. Fast and accurate choice responses to the tones were required. Although sequential effects in RTs were stable across all ISIs, the common first-order repetition effect in P300 amplitude was only observed at the 1.3-s ISI and not at the slower presentation rates. This dissociation between the first-order effects in RTs and ERPs speaks against an explanation of both effects by a common expectancy mechanism. In addition, sequential effects were observed as early as about 100 ms after stimulus onset in the lateralized readiness potential. Together with similar sequential effects in P300 latency, this finding supports a continuous flow model of information processing.

Event-related potentials (ERPs) and total time-frequency power analyses have shown that performance costs during task switching are related to differential preparation to switch tasks (switch cost) and repeat the same task (mixing cost) during both proactive control (cue-to-target interval; CTI) and reactive control (post-target). The time-frequency EEG signal is comprised of both phase-locked activity (associated with stimulus-specific processes) and nonphase-locked activity (represents processes thought to persist over longer timeframes and do not contribute to the average ERP). In the present study, we used a cued task-switching paradigm to examine whether phase-locked and nonphase-locked power are differentially modulated by switch and mixing effects in intervals associated with the need for proactive control (CTI) and reactive control (post-target interval). Phase-locked activity was observed in the theta and alpha bands, closely resembled that seen for total power, and was consistent with switch and mixing ERP positivities. Nonphase-locked analyses showed theta and alpha power effects for both switch and mixing effects early in the CTI and as well as more sustained alpha and beta activity around cue onset, and extending from mid-CTI into the post-target interval. Nonphase-locked activity in pretarget alpha and posttarget theta power were both correlated with response time mixing cost. These findings provide novel insight into phase-locked and nonphase-locked activity associated with switch and mixing costs that are not evident with ERP or total time-frequency analyses.

Recent aging studies on training in task switching found that older adults showed larger improvements to an untrained switching task as younger adults do. However, less clear is what type of cognitive control processes can explain these training gains as participants were trained with a particular type of switching task including bivalent stimuli, requiring high inhibition demands, and no task cues helping them keeping track of the task sequence, and by this, requiring high working-memory (WM) demands. The aims of this study were first to specify whether inhibition, WM, or switching demands are critical for the occurrence of transfer and whether this transfer depends on the degree of overlap between training and transfer situation; and second to assess whether practiced-induced gains in task switching can be maintained over a longer period of time. To this end, we created five training conditions that varied in switching (switching vs. single task training), inhibition (switching training with bivalent or univalent stimuli), and WM demands (switching training with or without task cues). We investigated 81 younger adults and 82 older adults with a pretest-training-posttest design and a follow-up measurement after 6 months. Results indicated that all training and age groups showed improvements in task switching and a differential effect of training condition on improvements to an untrained switching task in younger and older adults. For younger adults, we found larger improvements in task switching for the switching groups than the single-task training group independently of inhibition and WM demands, suggesting that practice in switching is most critical. However, these benefits disappeared after 6 months. In contrast, for older adults training groups practicing task switching under high inhibition demands showed larger improvements to untrained switching tasks than the other groups. Moreover, these benefits were maintained over time. We also found that the transfer of benefits in task switching was larger with greater overlap between training and transfer situation. However, results revealed no evidence for transfer to other untrained cognitive task. Overall, the findings suggest that training in resolving interference while switching between two tasks is most critical for the occurrence of transfer in the elderly.

In task switching, switch cost is the performance differences in task-switch and task-repetition trials. Recently, some researches have attempted to specify nature and origins of switch cost to uncover the mechanisms underlying task switching performance. Theoretically, there is disagreement as to whether switch cost actually represents the task-set reconfiguration or the task-set inertia. Many studies found that a prolonged preparation time reduces switch costs, which has been attributed to a task set reconfiguration process. However, unlike manipulations of preparation time, other studies varied the predictability of task sequence and found that the preparation benefit was the same for switches and repetitions. The aim of the present study was to investigate the effect of foreknowledge and preparation time on task switching. Two experiments were conducted in the present study. There were 30 participants (12 males and 18 females) volunteered to take part in experiment 1 and another 30 participants (9 males and 21 females) took part in experiment 2. In order to investigated the effect of foreknowledge on task switching, the experiment 1 was conducted with a 3 (foreknowledge type: no foreknowledge, part foreknowledge and full foreknowledge) × 2 (task type: switch task and repetition task) within-subject design. In the experiment 2, a 3 (preparation time: 100ms, 600ms and 1000ms) × 3 (foreknowledge type: no foreknowledge, part foreknowledge and full foreknowledge) × 2 (task type: switch task and repetition task) within-subject design was conducted to examined the mechanisms of effects of foreknowledge on task switching under the conditions of difference preparation time. The correct RT and switch cost were measured as the main index. The results showed that: (1) the amount of switch cost depend on foreknowledge, switch cost was smaller with full foreknowledge than with part and no foreknowledge, but not difference significantly between the later two. (2) The interaction between preparation time and foreknowledge was significant, and with increased preparation time, the effect of foreknowledge was more remarkable. Current findings suggest that the cognitive process that foreknowledge affected was task-set reconfiguration, rather than task-set inertia, and the effect was mediated by preparation time.

The cognitive mechanisms underlying deception: An event-related potential study

The temporal selectivity of additive factor effects on the reaction process revealed in ERP component latencies

Two four-choice reaction time (RT) experiments used the lateralized readiness potential (LRP) and the limb selection potential (LSP) to assess the effects of spatial S-R compatibility on motor processes. Individual stimuli were presented at one corner of a square centered at fixation, and each response was made with the left or right hand or foot. In Experiment 1, the correct response was determined by stimulus location, whereas in Experiment 2 it was determined by stimulus identity. Horizontal and vertical compatibility affected both RT and response accuracy, but the LRP and LSP results suggested that compatibility had little or no direct effect on the duration of motor processes. In addition, the results suggest that the relatively new LSP measure is a useful index of motor activation processes. Its insensitivity to horizontal stimulus artifacts makes it especially useful for studying the effects of horizontal spatial compatibility.